Internal combustion engine

ABSTRACT

An internal combustion engine includes a combustion chamber. The chamber includes a body that is movable in the chamber to vary the chamber volume and contains a catalyst. First valving is operable to admit an intake gas into the chamber and second valving connected with an aqueous fluid supply system is operable to admit an aqueous fluid and a steam reforming fuel into the chamber. A controller is configured to cause the second valving to admit a aqueous fluid and an amount of the steam reforming fuel into the chamber and when a predetermined condition exists in the chamber during compression of the intake gas to absorb heat generated by the compression of the intake gas in the presence of the catalyst to promote a steam reformation process to separate hydrogen from the steam reforming fuel or the aqueous fluid.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 15/022,944, filed Mar. 18, 2016, now U.S. Pat. No. 10,113,513,which is a 371 national phase filing of PCT Application No.PCT/GB2014/052879, filed Sep. 22, 2014, which claims the filing benefitsof GB patent application No. 1320857.4, filed Nov. 26, 2013, and GBpatent application No. 1316775.4, filed Sep. 20, 2013.

FIELD OF THE INVENTION

The invention relates to internal combustion engines and particularly,but not exclusively, to internal combustion engines for poweringautomotive vehicles.

BACKGROUND TO THE INVENTION

The reciprocating piston spark ignition engine is one known form ofinternal combustion engine used to power automotive vehicles.Reciprocating piston spark ignition engines comprise a number of pistonsarranged to reciprocate in respective cylinders and each connected to acrankshaft. Each of the cylinders is provided with inlet valving forcontrolling the inflow of air and fuel, exhaust valving for controllingthe exhaust of the products of combustion and a spark plug for ignitingthe air fuel mixture. Where the supply of fuel to the engine iscontrolled by a carburettor, the air and fuel are mixed in an intakemanifold upstream of the cylinders and the inlet valving comprises anintake valve that controls the intake of the fuel-air mixture into thecylinder. If the fuel supply to the cylinders is by fuel injection, theinlet valving comprises two valves. One of the valves is a fuel injectorand the other is an air intake valve. The fuel injector may be arrangedto inject fuel directly into the cylinder or may inject it into an airintake duct just upstream of the air intake valve.

Typically, reciprocating spark ignition engines operate a four-strokecycle. Each movement of a piston up or down its cylinder comprises onestroke of the four-stroke cycle. The four-stroke cycle consists of:

-   an induction stroke during which the inlet valving opens and air and    fuel are taken into the engine as the piston moves towards the    crankshaft;-   a compression stroke during which the inlet and exhaust valving are    closed and the air fuel mixture is compressed while the piston moves    away from the crankshaft;-   a power, or working, stroke during which the compressed mixture is    ignited and the rapid expansion caused by combustion of the mixture    forces the piston back towards the crankshaft; and-   an exhaust stroke during which the exhaust valving is open and the    exhaust gases are forced out of the cylinder as the piston moves    away from the crankshaft again.

Some reciprocating piston spark ignition engines operate a two-strokecycle, which is a variant of the four-stroke cycle. Such engines areusually of smaller capacity than four-stroke engines and in terms ofpassenger vehicles tend to be used for two-wheeled vehicles. Two strokeengines use ports located along the side of the cylinder instead ofvalves. As the piston moves up and down the cylinder, the ports arecovered and uncovered depending on where the piston is in the cylinder.In essence, in a two-stroke engine the induction and compressionprocesses take place during the first stroke and the combustion andexhaust processes take place during the second stroke.

The reciprocating piston compression ignition internal combustion engineis another form of engine commonly used to power automotive vehicles.Reciprocating piston compression ignition engines use a fuel having ahigher auto-ignition temperature than the fuels used by spark ignitionengines and operate a modified version of the four-stroke cycledescribed above. Specifically, during the induction stroke air is drawninto the cylinder and that air is compressed to a high pressure andtemperature during the compression stroke. Fuel is then injecteddirectly into the cylinder (or into a mixing chamber that leads into thecylinder) and combustion takes place as the fuel mixes with the hightemperature compressed air in the cylinder. Historically, reciprocatingpiston compression ignition engines were considered noisy and slow andin the automotive field were used mainly for trucks and other commercialvehicles such as buses. However in more recent times, high performancereciprocating piston compression ignition engines have been developedand now reciprocating piston compression ignition engines are commonlyused in small passenger vehicles such as saloon cars (sedans).

The Wankel engine is another form of spark ignition engine that has beenused to power automotive vehicles. The Wankel engine employs a four‘stroke’ cycle similar to the four-stroke cycle employed by thereciprocating piston spark ignition internal combustion engine. However,instead of reciprocating pistons, the Wankel engine has a roughlytriangular rotor that is mounted on an eccentric shaft for rotation inan approximately oval (epitrochoid-shaped) chamber. The ‘four strokes’take place in the spaces between the rotor and the chamber wall.

A common feature of these known internal combustion engines is that thefuel air mixture is input to a chamber in which it is combusted so thatthe rapid expansion of the mixture caused by the combustion actsdirectly on a body (piston or rotor) that is connected to an outputshaft so as to cause rotation of the shaft; the output of the enginebeing the rotation of the shaft.

An engine in which a body of liquid acts as the reciprocating piston hasalso been proposed.

SUMMARY OF THE INVENTION

The invention provides a method of operating an internal combustionengine as specified in claims 1-17. The invention also includes aninternal combustion engine as specified in claims 18-31.

BRIEF DESCRIPTION OF THE DRAWINGS

In the disclosure that follows, reference will be made to the drawingsin which:

FIG. 1 is a schematic representation of an internal combustion engine;

FIG. 2 is a schematic representation of an example of valving for theinternal combustion engine of FIG. 1;

FIG. 3 is a schematic representation of another example of valving forthe internal combustion engine of FIG. 1;

FIG. 4 is a schematic representation of an example of a controller forthe internal combustion engine;

FIG. 5 is a pressure-volume diagram illustrating a cycle of the internalcombustion engine of FIG. 1;

FIG. 6 is a temperature-entropy diagram illustrating the cycle of FIG.4;

FIG. 7 is a schematic representation of a modification of a part of theinternal combustion engine of FIG. 1;

FIG. 8 is a schematic representation of another internal combustionengine;

FIG. 9 is a schematic representation of an injector valve of theinternal combustion engine of FIG. 8; and

FIG. 10 is a schematic representation of a combustion initiator for theinternal combustion engines of FIGS. 1 to 4, 7 and 8.

DETAILED DESCRIPTION

Referring to FIG. 1, an internal combustion engine 10 comprises avariable volume combustion chamber 12 defined by a housing, or cylinder,having walls 14, 16, and a body that is movable in the chamber. In theillustrated example, the body is a reciprocating piston 18 that isconnected with a crankshaft 20 by a connecting rod 22.

The internal combustion engine 10 comprises first valving 24 operable toadmit an intake gas comprising an aspirant into the combustion chamber12. In the illustrated example, the intake gas is air received from anair supply system 26 connected with the first valving 24. The air supplysystem 26 may comprise a manifold configured to receive ambient air andconduct the air to the first valving 24. The first valving 24 maycomprise one or a plurality of valves connected with the air supplysystem 26. The air supply system 26 may comprise suitable filters toclean the air.

The internal combustion engine 10 comprises second valving 30 that isconnected with a steam supply system 32 and a reservoir 34 containing afuel for the internal combustion engine. The second valving 30 isoperable to admit steam from the steam supply system 32 and fuel fromthe reservoir 34 into the combustion chamber 12 as a mixture. As shownin FIG. 2, the second valving 30 may comprise one or a plurality offirst valves 36 that open into the combustion chamber 12 and one or moresecond valves 38 disposed between the steam supply system 32 and thefirst valve(s) 36 so as to isolate the first valves from the steamsupply system and permit it/them to admit fuel alone into the combustionchamber. In another example shown in FIG. 3, the second valving 30comprises one or a plurality of first valves 36 that open into thecombustion chamber 12 and are connected with the steam supply system 32and the reservoir 34 to admit the fuel-steam mixture into the combustionchamber and one or plurality of second valves 38 that open into thecombustion chamber 12 and are separately connected to the reservoir 34and isolated from the steam supply system to allow it/them to admit fuelinto the combustion chamber independently of the first valve(s).

The internal combustion engine 10 is provided with an exhaust system 40and exhaust valving 42 comprising at least one exhaust valve that isoperable to release exhaust gases from the combustion chamber 12 intothe exhaust system. In the illustrated example, the exhaust system 40 iscooperable with the steam supply system 32 to extract heat from exhaustgases flowing in the exhaust system to provide at least a part of theheat used to produce the steam. This may, for example, be achieved byhaving piping through which the exhaust gases flow winding around a pipeor a vessel in which the steam is produced or flowing the exhaust gasesthrough a vessel containing one or more steam pipes.

The internal combustion engine 10 comprises a controller 48 to controlthe operation of the first valving 24, second valving 30 and exhaustvalving 42. In the illustrated example, the first valving 24, secondvalving 30 and exhaust valving 42 comprise electrically actuated valves,for example solenoid valves, that are opened and closed in response toelectrical command signals issued by the controller 48. In otherexamples, at least one of the first valving 24, second valving 30 andexhaust valving 42 may include one or more valves that are hydraulicallyor pneumatically actuated in response to electrical command signalsissued by the controller 48 to a source of hydraulic or pneumaticactuating fluid.

The internal combustion engine 10 further comprises one or more sensors50 connected with the controller 48 to provide the controller withsignals indicative of the pressure/temperature in the combustion chamber12. The sensor(s) 50 may be a pressure sensor(s) or a temperaturesensor(s). The sensor(s) 50 may be any suitable type of sensor capableof operating at the relatively high temperatures that will beencountered in use of the internal combustion engine 10. For thepurposes of controlling operation of the internal combustion engine 10,at least during some phases of its operation, the temperature sensor(s)need to be highly responsive to temperature changes taking place withinthe combustion chamber 12. The temperature sensor(s) may be an infraredtemperature sensor(s) that senses the temperature in the combustionchamber through a translucent window (not shown). Alternatively, forexample, a high temperature embedded photodiode such as is disclosed inU.S. Pat. No. 5,659,133 (the content of which is incorporated herein byreference) could be used.

The internal combustion engine 10 may be provided with a combustioninitiator 52 to assist in initiating combustion events in the combustionchamber 12. The combustion initiator 52 may be an electrical combustioninitiator such as a glow plug, hot wire, spark plug or the like.

A catalyst 54 is mounted in the combustion chamber 12 by any convenientmethod. The catalyst 54 may, for example, be mounted in a mountingcomprising suitable recessing provided in the wall 14 so that it doesnot affect the volume of the combustion chamber 12.

The catalyst 54 may alternatively, or additionally, be mounted on thecrown of the piston 18, preferably in a mounting comprising suitablerecessing as shown in FIG. 1. Mounting the catalyst 54 on the piston isnot currently preferred as it increases the inertia of the piston. Inanother example, the catalyst may instead, or additionally, be mountedon the first valve(s) 36. Examples of catalyst mounting on an injectorvalve are described below with reference to FIGS. 8 and 9. In anotherexample, the catalyst may instead, or additionally, be provided on acombustion initiator 52. Examples of catalyst mounting on a combustioninitiator are described below with reference to FIG. 10.

In FIG. 1, the connections between the controller 48 and the valving 24,30, 42 and the sensor(s) 50 are not shown. This is simply for the sakeof clarity of illustration and the skilled person will have nodifficulty in envisaging suitable ways and means for making theconnections.

In FIG. 1, the internal combustion engine 10 is shown comprising justone combustion chamber 12. While this may be appropriate for someapplications, typically the internal combustion engine 10 will comprisea plurality of combustion chambers 12, each having a piston 18 connectedto the crankshaft 20. In a multiple chamber, or cylinder, engine, thechambers may be arranged in any suitable known configuration such asin-line, flat or a V.

Referring to FIG. 4, a suitable controller 48 for the internalcombustion engine 10 may comprise one or more a processors 1600 andsignal conditioning components 1602 for, for example, amplifying signalsand converting analogue signals to digital and digital signals toanalogue to permit the controller to receive and use signals from thesensor(s) 54 and output usable signals to the valving 24, 30, 42 andother components of the internal combustion engine 10 that may becontrolled by the controller. The controller 48 may additionallycomprise one or more random access memories (RAM) 1604 for storing datagenerated during operation of the internal combustion engine andcircuitry 1606 for use in sampling incoming signals from one or moresensors to provide a usable input for the processor. The control unit728 may additionally comprise one or more data storage components in theform of permanent memory 1606, which may be a read only memory (ROM), inwhich one or more control software portions 1608 are permanently stored.Of course, for some applications, no permanent memory is required. Forexample, the controller may be connected with a master computer in whichthe control algorithms are stored and which uploads them to a RAM in thecontroller at start up of the controller. Another alternative would befor the controller to be slaved to a master controller or computer. Yetanother alternative would be for the controller to comprise one or morehard wired control circuits.

The internal combustion engine 10 may operate on a modified dieselcycle. Operation of the internal combustion engine 10 using a modifieddiesel cycle will now be described with reference to FIGS. 5 and 6.

Referring to FIGS. 5 and 6, point 1 indicates the start of an operatingcycle of the internal combustion engine 10. At point 1, the piston 18 isat one end of its reciprocating stroke (the lowermost position as viewedin FIG. 1). This is commonly referred to as bottom dead centre (BDC)position, even in cases in which the engine cylinders are orientatedhorizontally such as in a flat four. At this stage, exhaust gases from aprevious cycle have been substantially removed from the combustionchamber 12 and a fresh charge of intake gas at ambient pressure andtemperature has been admitted by operation of the exhaust valving 42 andfirst valving 24 respectively. The first valving 24 and exhaust valving40 are closed. The intake gas is at a first pressure P₁ and firsttemperature T₁. The piston 18 then moves from BDC towards the wall 14.As the piston moves towards the wall 14, it reduces the volume of thecombustion chamber 12 and in so doing, it compresses the intake gas. Thecompression of the intake gas raises its pressure and temperature fromP₁, T₁. The internal combustion engine 10 is configured so that when thepiston 18 reaches the opposite end of its stroke at which it is closestto the wall 14, commonly referred to as the top dead centre (TDC)position, the volume of the combustion chamber 12 is reducedsufficiently for the intake gas to have been compressed to apredetermined pressure P₂. The TDC position is indicated at position 2b.

As shown in FIGS. 5 and 6, as the pressure of the intake gas rises fromthe pressure P₁ at point 1, its temperature initially risescorrespondingly from temperature T₁, which may typically be around 293°K. When a predetermined pressure/temperature P_(2a)/T_(2a) indicated atpoint 2 a is achieved, the controller 48 issues signals to cause thesecond valving 30 to open and admit a metered mixture of fuel and steaminto the combustion chamber 12. The admission of the fuel and steammixture into the hot intake gases in the presence of the catalystpromotes a steam reformation process by which hydrogen is separated fromthe fuel or the steam. The hydrogen is combusted in the combustionchamber 12 at a later stage in the cycle. The steam and fuel absorb heatfrom the compressed intake gases due to the steam reforming processthereby cooling the intake gases. In the illustrated example, the fueland steam mixture is admitted at a metered rate that cools the intakegases sufficiently to maintain a substantially constant temperature asthe compression of the intake gases continues from point 2 a to point 2b so that, as shown in FIG. 6, the temperatures T_(2a) and T_(2b) are atleast substantially equal. Point 2 b indicates the point at which thepiston has reached TDC and is ready for the expansion stroke in which itreturns to BDC. At point 2 b, the controller 40 issues signals to causethe second valving 30 to cease admitting steam to the combustion chamber12 and to admit a metered charge of fuel into the combustion chamber forthe combustion process.

At point 2 b, the pressure P_(2b) and temperature T_(2b) in thecombustion chamber 12 are such that the hydrogen and fuel shouldspontaneously ignite. Where a glow plug, hot wire or the like 52 isprovided to assist in initiating the combustion of the hydrogen andfuel, the controller 48 is configured to issue a signal to an electricalpower source (not shown) to cause the glow plug, hot wire or the like tobe energised at the same time as, or shortly after, the issue of thesignal to cause the second valving 30 to cease admitting steam and toadmit the metered charge of fuel into the combustion chamber 12. Thecombustion of the fuel and hydrogen in the combustion chamber 12 causesthe piston 18 to be driven from the TDC position back towards the BDCposition. The movement of the piston is transmitted to the crankshaft 20by the connecting rod 22 to turn the crankshaft and provide work outputW from the internal combustion engine 10. In the illustrated example,the fuel is admitted into the combustion chamber 12 at a metered rateselected so that the combustion of the fuel and hydrogen takes placeunder substantially constant pressure conditions. The metered fuel isadmitted during the period between points 2 b and 3 in FIGS. 5 and 6.

At point 3, which may be determined as a predetermined elapse of timefrom point 2 b or when a predetermined pressure/temperature is detectedby the sensor(s) 54, the controller 48 issues a signal causing thesecond valving 30 to cease admitting fuel to the combustion chamber 12.The combustion gases continue expanding as the piston 18 moves towardsthe BDC position and the pressure and temperature in the combustionchamber progressively fall towards point 4, which represents the BDCposition. At point 4, which may be indicated by a pressure/temperatureP₄/T₄ detected by the sensor(s) 54, the controller 48 issues a signal tocause the exhaust valving 42 to open to release the combustion gases(exhaust gases) into the exhaust system 40. As the exhaust gases arereleased from the combustion chamber 12, the pressure in the chamberrapidly falls towards ambient pressure. At this stage, the first valving24 is caused to open to admit a fresh charge of intake gases and theoperational cycle is back at point 1 and ready for the next cycle. Theexhaust valving 42 may remain open, at least initially, following theopen of the first valving 24 to allow chamber scavenging by the incomingintake gas.

The above-described cycle harvests heat generated during the compressionstroke to produce additional fuel in the form of hydrogen produced bysteam reformation. This additional fuel increases the cycle performance.The overall amount of fuel that is combusted between points 2 b and 3 inFIGS. 5 and 6 is the fuel injected during the compression stroke betweenpoints 2 a and 2 b, less the fuel consumed in the steam reformationprocess, plus the hydrogen fuel generated by the steam reformationprocess and the fuel admitted into the combustion chamber between points2 b and 3. In total that combination should have a higher calorificvalue than the fuel admitted between points 2 a and 3 as the hydrogengenerating reactions are endothermic in total. If the same amount ofsupplied fuel were supplied to a standard diesel cycle, the fuel wouldbe admitted to the combustion chamber between points 2 and 3 in FIGS. 5and 6. It can be seen that the indicated work (area of the P-V diagramshown in FIG. 5) for the modified diesel cycle (points 1 to 2 a to 2 bto 3 to 4 to 1) is larger for the same amount of admitted fuel as in acomparable standard diesel cycle (points 1 to 2 to 3 to 4 to 1), hencethe superior efficiency of the modified diesel cycle.

The efficiency improvement provided by the modified diesel cycleillustrated by FIGS. 5 and 6 can be evaluated by considering the workand heat energies for each stage as follows:

Isentropic compression (point 1 to point 2 a):₁ W _(2a) =mc _(v)(T _(2a) −T ₁)₁ Q _(2a)=0  (3)

Isothermic compression (point 2 a to point 2 b):

$\begin{matrix}{{{{\,\mspace{76mu}}_{2a}W_{2b}} = {{mRT}_{{2a},{2b}}\mspace{14mu}{\ln\left( \frac{V_{2b}}{V_{2a}} \right)}}}{{{}_{2a}^{}{}_{2b}^{}} = {{{}_{2a}^{}{}_{2b}^{}}\mspace{14mu}\left( {{the}\mspace{14mu}{heat}\mspace{14mu}{that}\mspace{14mu}{is}\mspace{14mu}{absorbed}\mspace{14mu}{by}\mspace{14mu}{steam}\mspace{14mu}{reforming}} \right)}}} & (4)\end{matrix}$

Isobaric combustion (point 2 b to point 3):_(2b) W ₃ =P _(2b,3)(V ₃ −V _(2b)) _(2b) Q ₃ =mc _(p)(T ₃ −T _(2b)) tm(5)

Isentropic expansion (point 3 to point 4):₃ W ₄ =mc _(v)(T ₄ −T ₃) ₃ Q ₄=0  (6)

Scavenging (4->1):₄ W ₁=0 ₄ Q ₁ =mc _(v)(T ₁ −T ₄)  (7)

The efficiency is then evaluated as the net work over spent heat:

$\begin{matrix}{\eta = \frac{{{{}_{}^{}{}_{2a}^{}}{\,{+_{2a}W_{2b}}}} + {{}_{2b}^{}{}_{}^{}} + {{}_{}^{}{}_{}^{}} + {{}_{}^{}{}_{}^{}}}{{{}_{2a}^{}{}_{2b}^{}} + {{}_{2b}^{}{}_{}^{}}}} & (8)\end{matrix}$

(note that _(2a)Q_(2b) is negative).

A comparable standard Diesel cycle (of the same maximum pressure andvolume) would have the efficiency:

$\begin{matrix}{\eta = \frac{{{}_{}^{}{}_{}^{}} + {{}_{}^{}{}_{}^{}} + {{}_{}^{}{}_{}^{}}}{{}_{}^{}{}_{}^{}}} & (9)\end{matrix}$

For a compression ratio of 1:25, ambient STP conditions, a point 2 a(catalytic) temperature of 700K, methane as the fuel and stoichiometriccombustion, a theoretical cycle efficiency improvement from 66% to 75%is obtained. It is to be understood that methane is given purely as anexample of a suitable fuel and that in principle any suitablehydrocarbon may be used with butane, ethanol, methanol and propane (inno particular order) all being considered good fuels for steamreforming. Conventional internal combustion engine fuels such as dieseland petrol (gasoline) may also be used.

The temperature T_(2a) at point 2 a at which fuel is admitted into thecombustion chamber 12 during the compression stroke is selected as theminimum temperature that will suffice for a significant amount of steamreformation to occur. It is desirable to make this temperature T_(2a) aminimum as this allows for more heat from the compression stroke to beabsorbed, which allows a higher compression ratio to be obtained for thesame maximum pressure P_(2b). The temperature T_(2a) selected can befound empirically and may represent a compromise between obtaining areasonable amount of steam reformation and absorbing additional heat.Another factor to be taken into account in determining the temperatureT_(2a) is the rate of the catalysed reaction, which increases withtemperature and may place a limit on how low the temperature T_(2a) maybe if a significant amount of steam reformation is to occur. In generalit can be expected that larger engines operating at lower speeds will beable to accommodate a wider selection of catalysts or lower point 2 atemperatures.

Another potential advantage of the modified diesel cycle illustrated byFIGS. 5 and 6 is that obtaining higher efficiencies without elevatingthe maximum operating temperature of the internal combustion engine 10produces, in effect, a reduction in pollution generated for the poweroutput. In addition, because hydrogen combustion is involved, it is tobe expected that the emission levels of carbon monoxide (CO) andhydrocarbons (HC) will be very low compared to a conventional dieselengine.

Yet another advantage of the modified diesel cycle is that the heatabsorption by the steam reforming process may result in a lowertemperature T2 b in the combustion chamber at the end of the compressionstroke than the temperature T2 in a comparable conventional dieselengine (compare points 2 b and 2 in FIG. 6). Since nitrous oxide(NO_(x)) production depends exponentially on temperature, the NO_(x)emission level of an internal combustion engine 10 operating themodified diesel cycle should be very low, at least compared with anengine running a conventional diesel cycle.

FIG. 7 shows a modified form of the internal combustion engine of FIGS.1 to 4. In FIG. 7 components that are the same as, or similar to,components shown in FIG. 1 are indicated by the same reference numeralsincremented by 100 and may not be described again. The differencebetween the internal combustion engine 110 and the internal combustion10 is that it has a second reservoir 170. The first reservoir 134 isused to hold a steam reforming fuel for the steam reforming process thatis admitted into the combustion chamber 112 between points 2 a and 2 b(FIGS. 5 and 6) of the compression stroke for consumption in the steamreforming process. The second reservoir 170 holds a combustible fuelthat is admitted into the combustion chamber 112 during the combustionphase between points 2 b and 3 (FIGS. 5 and 6). In this example, thesecond valving 130 comprises at least one first valve 136 connected withthe steam supply system 132 and first reservoir 134 to admit thefuel-steam mixture into the combustion chamber and at least one secondvalve 138 connected with the second reservoir 170 to admit the fuel intothe combustion chamber. The first valve(s) 136 may comprise an injectorvalve fitted with a catalyst, for example, as described below withreference to FIGS. 8 and 9. The internal combustion engine 110 may beprovided with a combustion initiator that carries a catalyst for thesteam reformation process, for example, a glow plug as described belowwith reference to FIG. 10.

The configuration illustrated by the example shown in FIG. 7 allows thepossibility of supplying one fuel for the steam reforming process and adifferent fuel for the combustion process so that a fuel that might beexpected to give better hydrogen yields for the steam reforming processcan be selected where it is desirable to use a different fuel for thecombustion process, for example for efficiency or availability reasons.Thus, for example, in some examples a fuel with limited availabilitysuch as a relatively cheap bio-waste fuel may be used as the steamreforming fuel for the steam reforming process and a more readilyavailable fuel, for example diesel or petrol (gasoline) may be used asthe combustible fuel for the combustion process. Similarly, a ‘light’fuel such as methanol or methane may be used as the steam reforming fuelfor the steam reforming process since it may produce greaterefficiencies, while a more readily available heavier fossil fuel such asdiesel or petrol may be used as the combustible fuel for the combustionprocess.

FIGS. 8 and 9 show features of another internal combustion engine 210.Parts of the internal combustion engine 210 similar to or the same asparts of the internal combustion engine 10 are indicated by the samereference numeral incremented by 200 and may not be described again.

Referring to FIG. 8, an internal combustion engine 210 comprises acombustion chamber 212 defined by walls 214, 216. The combustion chamber212 houses a reciprocating piston 218 that is connected with acrankshaft (not shown) by a connecting rod (also not shown). Theinternal combustion engine 210 further comprises first valving 224 toadmit an intake gas comprising an aspirant into the combustion chamber.The first valving 224 may be connected to an air supply system 226. Theinternal combustion engine 210 further comprises second valving 230comprising at least one injector valve 236. Purely for ease ofpresentation, in the description that follows, references to theinjector valve 236 will be in the singular. This is not to be taken aslimiting as multiple injector valves 236 may be provided.

The injector valve 236 is connected with a reservoir via a fuel pump254. The reservoir 252 is to hold a combustible fuel and the fuel pump254 is operable to pump the fuel to the injector valve. The reservoir252 and fuel pump 254 may a standard reservoir and fuel pump suppliedwith the internal combustion engine 210. The injector valve 236 is alsoconnected with a second reservoir 256 via a pump 258. The pump 258 isoperable to pump an aqueous fluid or a mixture comprising an aqueousfluid and a steam reforming fuel to the injector valve 236.

Referring to FIG. 9, the injector valve 236 comprises a valve body 270configured to be inserted into an injector port 272 defined in the wall214. The valve body 270 has a first, or outlet, end provided with aplurality of outlet apertures 274 and a second end provided with aflange 276. A keeper plate 278 may be secured to the wall 214 by screws,bolts or the like 280. The first injector valve 276 is configured to beengaged by the keeper plate 278 such that it is secured to the wall 214by a pressing force applied by the keeper plate. A suitable seal 282 maybe disposed between the flange 276 and wall 214 so as to be compressedand seal between them.

The injector valve 236 has an inlet head 284 extending from the side ofthe flange 276 opposite the side from which the valve body 270 extends.The inlet head 284 has connector parts 286, 288 for connection torespective pipes 290, 292 (FIG. 8) that connect the injector valve 236with the pumps 254, 258.

The injector valve 236 carries a catalyst 254 for the steam reformationprocess that takes place in the combustion chamber 212 when operating acycle incorporating a steam reformation process such as a modifieddiesel cycle the same as, or similar to, the modified diesel cycledescribed above with reference to FIGS. 5 and 6. The catalyst 254 may beprovided in the form of a sleeve 290 secured to the outlet end of thevalve body 270. The sleeve 290 may be a cylindrical member defining afully enclosed flow path extending from the outlet end of the valve body270. Alternatively, the sleeve 290 may, for example, be a partial sleeveprovided with a side opening(s), which may, for example, be a lengthwaysextending slit(s). At the least some of the outlet apertures 274 may beconfigured to direct a spray of the output fluid directly onto thecatalyst 254.

An injector valve carrying a catalyst, for example as illustrated inFIG. 9, may be provided in newly built engines. This provides thepossibility configuring an engine to operate a cycle incorporating asteam reformation process, such as the modified diesel cycle describedabove with reference to FIGS. 5 and 6, without the need to reconfigure,or specially configure, the combustion chamber to receive a mounting fora catalyst. Such injector valves may also be used to provide arelatively straightforward means of adapting existing internalcombustion engines to operate the modified diesel cycle. One or moreinjector valves carrying a catalyst may, for example, be supplied as akit for retrofitting to an existing internal combustion engine in placeof one or more standard injector valves. The kit may include a reservoiror a pump, such as the reservoir 256 and pump 258, with suitable pipingto connect the injector valve(s) to the pump.

In the example by FIGS. 8 and 9, a catalyst is provided on an injectorvalve that is operated to admit an aqueous fluid, or a steam reformingfuel or a mixture comprising aqueous fluid and steam reforming fuel intothe combustion chamber during the compression phase of a combustioncycle. This is not essential. The catalyst may be provided on aninjector valve that is operable to admit the aspirant or the fueladmitted during the combustion phase of the cycle. In each case, thevalve may be configured so that the catalyst it carries is exposed tothe aqueous fluid, steam reforming fuel and heat in the combustionchamber so that it can function as a catalyst for the steam reformationprocess.

In the example illustrated above, the injector valve has respectiveconnector parts for separate pipes by which the injector valve isconnected to the reservoirs via the two pumps. In another example, amanifold or the like may be provided upstream of the injector valve toreceive supplies from the reservoirs via their pumps so that theinjector valve can have a single connector part by which the injectorvalve is connectable to the manifold or the like by a single pipe.

In other examples, internal combustion engine such as those illustratedby FIGS. 1 to 4, 7 and 8 and 9, may be provided with a combustioninitiator carrying a catalyst. The combustion initiator may take theform of an electrical combustion initiator such as a glow plug, hot wireor spark plug. Referring to FIG. 10, an electrical combustion initiatorin the form of a glow plug 452 may comprise a threaded body part 490configured to permit the combustion initiator to be screwed into asuitably threaded port defined in a wall of a combustion chamber. Theglow plug 452 may comprise a flange 492 configured to be engaged by atightening tool, such as a wrench socket, to permit the combustioninitiator to be firmly screwed into such a port. The glow plug 452 maycomprise an electrical input terminal 494 configured to permit the glowplug to be electrically connected with a suitable electrical powersource (not shown). Electrical power sources and connections betweensuch sources and electrical combustion initiators in internal combustionengines will be familiar to those skilled in the art and will notdescribed in herein. The glow plug 452 may further comprise a centreelectrode 496 electrically connected with the input terminal 494 andheating and regulating coils 498, 500. The heating and regulating coils498, 500 are encased in insulation powder 502 contained in a sheath ortube 504 disposed at the end of the glow plug 452 opposite the end atwhich the input terminal 494 is situated. The sheath 504 extendscoaxially from an end of the body part 490. The sheath 504 functions asan energy output member and in use is disposed in the combustion chamberso that it is exposed to the fuel, hydrogen and air mixture in thecombustion chamber and can add energy to the mixture in the form ofheat. The glow plug 452 may at least assist in initiating combustion, atleast during start up of the internal combustion engine 210 when thewalls 214, 216 are relatively cold and may absorb a significant amountof the heat generated during compression of the intake gases.

The glow plug 452 further comprises a catalyst 454 for a steamreformation process that takes place in the combustion chamber when asteam reforming fuel and aqueous fluid are admitted to the chamberduring compression of the intake gases. In the illustrated example, thecatalyst 454 is a member 506 secured to the body part 490 of the glowplug. The member 506 may extend coaxially with the body part 490 andsheath 504 and is positioned such that when the glow plug 452 isinstalled, the catalyst is exposed to the aqueous fluid, heat and steamreforming fuel in the combustion chamber 212. The member 506 may be asleeve surrounding the sheath 504 over a part of its length.Alternatively, the member 506 may, for example, be a partial sleeveprovided with side openings to ensure the sheath 504 is not overlyshielded from the fluids in the combustion chamber 212. In anotherexample, the catalyst may be provided in the form of a plurality ofmembers secured to the glow plug 452 or may be plated onto a part of theglow plug.

As with examples in which an injector valve comprises a catalyst,providing a combustion initiator with a catalyst provides a relativelystraightforward means of adapting existing internal combustion enginesto incorporate a steam reformation process into their operating cycle.Of course, a combustion initiator provided with a catalyst may be usedin a new build engine that is designed to incorporate a steamreformation process in its operating cycle.

A combustion initiator(s) provided with a catalyst may be used inconjunction with an injector valve(s) provided with a catalyst, whichmay the same or a different catalyst, and supplied in a kit withreservoir and pump as previously described. Similarly, an injectorvalve(s) or combustion initiator(s) provided with a catalyst may be usedin conjunction with catalysts mounted in the combustion chamber and mayeach be the same or different catalysts.

A kit for retrofitting to an existing internal combustion engine mayadditionally comprise control circuitry or instructions to modify theoperation of the engine controller of the engine to configure it tooperate a new cycle incorporating a steam reformation process. Thecontrol circuitry may take the form of, for example, an additionalcircuit board(s) to be plugged into the controller, a replacementcircuit board(s) or a processor device loaded with the instructions.Alternatively, in other examples the kit may comprise a data carrierthat can be temporarily connected with an engine controller to allow newinstructions to be loaded onto the controller by way of a firmwareupgrade or software update to memory.

In some examples, it may be desirable to provide discontinuities in thesurface of the catalyst as a means of increasing the surface area ofcatalyst material exposed to the steam in the combustion chamber. Thecatalyst may for example be provided with surface grooves or ridges, orother discontinuities such as discrete projections or depressions thatmay have a circular, irregular or other shaped cross-section.

It will be understood that providing a catalyst for a steam reformationprocess on a combustion initiator or injector valve may be advantageousin that it allows the possibility of providing the catalyst by simplyfixing replacement parts in existing ports provided in the combustionchamber walls. Thus an existing internal combustion engine can beconverted to incorporate a steam reformation process into its operatingcycle with no changes made to the engine block or cylinder head.Alternatively, it may be advantageous to maximise the catalyst surfacearea by providing a catalyst in one or more recesses in the combustionchamber walls, on an injector valve(s) and on a combustion initiator(s).

In the illustrated examples, the steam and steam reforming fuel areadmitted into the chamber via separate valves and mix in the injectionzone in the chamber or are injected through a common injector so that acertain amount of mixing may take place upstream of the chamber. Forcertain examples, a mixing chamber may be provided upstream of thesecond valving so that the steam and steam reforming fuel can besupplied to the second valving as a mixture.

In the illustrated examples, a combination of an aqueous fluid and asteam reforming fuel is admitted into the combustion chamber during thecompression stroke to promote a steam reforming process to separatehydrogen from the steam reforming fuel or steam to be combusted in thecombustion chamber. In other examples, the aqueous fluid may be in theform of a water mist or a combination of water mist and vapour.

In the illustrated examples, the steam reforming fuel for the steamreforming process may be a non-aqueous hydrogen containing compound,hydrocarbon or fossil fuel. The same fuel may serve as the steamreforming fuel and the combustible fuel. Alternatively, the steamreforming and combustible fuels may be different. In general, the steamreforming fuel may be any fluid that can be injected into the chamberduring the compression phase, or stroke, of the engine to reactexothermically with oxygen; that is release energy when oxidised. Insteam reforming the steam reforming fuel may be oxidised by the oxygenin the water (steam), thereby releasing hydrogen from the water (steam)or steam reforming fuel, it being understood that hydrogen may bereleased from both. In addition to the fuels previously mentioned, otherfuels that may be used for the steam reforming fuel including hypergolicfuels, hydro peroxide and boranes such as diborane, pentaborane anddecaborane.

It is to be understood that the steam reforming fuel is not necessarilycombustible. However, if the steam reforming fuel is combustible, anyresidue from the steam reforming process can be burnt during thecombustion process.

It is to be understood that while steam reforming is the predominanthydrogen separation process that takes place in the chamber, there mayalso be some hydrogen separated from the water (steam) by dissociation.

Due to the relatively high levels of water vapour present in thecombustion chamber during the combustion process, the exhaust gasesreleased from the combustion chamber will contain significant amounts ofwater vapour. In some examples, one or more condensers may be providedin the exhaust system to condense the water vapour for reuse as theaqueous fluid in subsequent engine cycles.

It will be understood that the best catalyst for a particular internalcombustion engine and steam reforming fuel may be determined by testing.It is currently envisaged that Cu/ZnO, Pd/ZnO, CuZrO₂ or compositealloys of these will be suitable catalysts. The catalyst selected willneed to have sufficient thermal durability to withstand use in acombustion environment.

In the illustrated examples, the body partially defining the variablevolume chamber is a reciprocating piston. In other examples, the bodymay be a rotary member. The description of the illustrated examplesrefers to the use of a pressure/temperature sensor(s) to provide thepressure/temperature indications that cause the controller to issuesignals to cause the injection of the aqueous fluid and non-aqueoushydrogen containing compound during the compression stroke. In someexamples, particularly in slower moving engines, a position sensor(s)detecting the position of the body in the combustion chamber, forexample the piston 18, may be used. Thus, for example two positionsensors spaced apart in the direction of movement of the piston may beused to provide an indication of the direction of movement of thepiston, with the second sensor indicating that the piston has reached aposition at which the volume of the chamber will be such that thepressure/temperature is the desired pressure/temperature at whichinjection should occur.

Although not limited to such applications, it is envisaged that internalcombustion engines operating a modified diesel cycle as illustrated byFIGS. 5 and 6 will be suitable for applications in the automotiveindustry. While the structure and operating principles described abovemay be advantageously applied to newly built internal combustionengines, it is to be understood that existing engines may be modified byto obtain the benefits of the invention.

The invention claimed is:
 1. A method of operating an internalcombustion engine that comprises a housing and a movable body that forma combustion chamber that has a single enclosed volume that is variableby movement of said movable body relative to said housing, and acatalyst contained in said single enclosed volume, said methodcomprising: at a first pressure in said single enclosed volume admittingan intake gas comprising an aspirant into said single enclosed volume;moving said body relative to said housing to reduce the volume of saidsingle enclosed volume to compress said intake gas to raise pressure insaid single enclosed volume from said first pressure to a secondpressure that is greater than said first pressure; admitting an aqueousfluid and a steam reforming fuel into said single enclosed volume whenthe pressure in said single enclosed volume reaches a predeterminedpressure intermediate said first and second pressures so that saidaqueous fluid and steam reforming fuel absorb heat generated by saidcompression of said intake gas and said catalyst promotes a steamreformation process by which hydrogen is separated from said steamreforming fuel or said aqueous fluid; and when the pressure in saidsingle enclosed volume is at least at said second pressure, admitting acombustible fuel into said single enclosed volume and combusting saidcombustible fuel and hydrogen, wherein combusting said combustible fueland hydrogen causes movement of said movable body relative to saidhousing to increase the volume of said single enclosed volume and saidmovement of said movable body provides an energy output of saidcombustion chamber.
 2. A method of operating an internal combustionengine as claimed in claim 1, comprising admitting said aqueous fluidand steam reforming fuel into said single enclosed volume as a mixture.3. A method of operating an internal combustion engine as claimed inclaim 1, comprising controlling the admission of said aqueous fluid orsaid aqueous fluid and steam reforming fuel into said single enclosedvolume so that the temperature within said chamber remains substantiallyconstant.
 4. A method of operating an internal combustion engine asclaimed in claim 1, comprising admitting said aqueous fluid into saidsingle enclosed volume as a water mist, vapour or a combination of watermist and vapour.
 5. A method of operating an internal combustion engineas claimed in claim 1, comprising releasing exhaust gases generated bycombustion of said combustible fuel and hydrogen from said combustionchamber and extracting heat from said released exhaust gases to heatsaid aqueous fluid prior to admission of said aqueous fluid to saidsingle enclosed volume.
 6. A method of operating an internal combustionengine as claimed in claim 1, comprising controlling the admission ofsaid combustible fuel into said single enclosed volume so that asubstantially constant pressure is maintained during at least a firstphase of combustion of said combustible fuel and hydrogen.
 7. A methodof operating an internal combustion engine as claimed in claim 1,wherein said body comprises: i) a reciprocating piston; or ii) a rotarymember.
 8. A method of operating an internal combustion engine asclaimed in clam 7, wherein said catalyst is carried by saidreciprocating piston or rotary member.
 9. A method of operating aninternal combustion engine as claimed in claim 1, wherein said catalystis provided on at least one of: i) an injector by which said steamreforming fuel or combustible fuel is admitted into said single enclosedvolume; ii) a combustion initiator provided to initiate combustion ofsaid combustible fuel and hydrogen; and iii) a wall of said combustionchamber.
 10. A method of operating an internal combustion engine asclaimed in claim 1, wherein said steam reforming fuel and combustiblefuel are the same.
 11. A method of operating an internal combustionengine that comprises a combustion chamber having a volume defined by ahousing and a reciprocating piston that in use reciprocates relative tosaid housing between a top dead center position and a bottom dead centerposition to vary said volume and a catalyst provided on said piston,said method comprising: admitting an intake gas comprising an aspirantinto said combustion chamber; reducing the volume of said combustionchamber to compress said intake gas by moving said piston relative tosaid housing towards said top dead center position to raise pressure insaid housing from a first pressure to a second pressure; injecting anaqueous fluid and a steam reforming fuel into said intake gas in saidcombustion chamber when the pressure in said combustion chamber reachesa predetermined pressure intermediate said first and second pressuresand said piston is disposed intermediate said top dead center and bottomdead center positions so that said aqueous fluid and steam reformingfuel absorb heat generated by said compression of said intake gas andsaid catalyst promotes a steam reformation process by which hydrogen isseparated from said steam reforming fuel or said aqueous fluid; and whenthe pressure in said combustion chamber is at least at said secondpressure, admitting a combustible fuel into said combustion chamber andcombusting said combustible fuel and hydrogen, wherein combusting saidcombustible fuel and hydrogen causes movement of said piston relative tosaid housing towards said bottom dead center position to increase thevolume of said combustion chamber and said movement of said body towardssaid bottom dead center position provides an energy output of saidcombustion chamber, and wherein said aqueous fluid and steam reformingfuel are injected into said combustion chamber when said volume ispartially defined by a wall of said housing that is sealingly engaged bysaid piston.
 12. A method of operating an internal combustion engine asclaimed in claim 11, comprising admitting said aqueous fluid and steamreforming fuel into said combustion chamber as a mixture.
 13. A methodof operating an internal combustion engine as claimed in claim 11,comprising controlling the admission of said aqueous fluid or saidaqueous fluid and steam reforming fuel into said combustion chamber sothat the temperature within said chamber remains substantially constant.14. A method of operating an internal combustion engine as claimed inclaim 11, comprising admitting said aqueous fluid into said chamber as awater mist, vapour or a combination of water mist and vapour.
 15. Amethod of operating an internal combustion engine as claimed in claim11, comprising releasing exhaust gases generated by combustion of saidcombustible fuel and hydrogen from said combustion chamber andextracting heat from said released exhaust gases to heat said aqueousfluid prior to admission of said aqueous fluid to said combustionchamber.
 16. A method of operating an internal combustion engine asclaimed in claim 11, comprising controlling the admission of saidcombustible fuel into said combustion chamber so that a substantiallyconstant pressure is maintained during at least a first phase ofcombustion of said combustible fuel and hydrogen.
 17. A method ofoperating an internal combustion engine as claimed in claim 11, whereinsaid steam reforming fuel and combustible fuel are the same.
 18. Aninternal combustion engine comprising: a housing and a body movable insaid housing, said body and housing defining a combustion chamber thathas a single enclosed volume that is variable by movement of said bodyrelative to said housing; a catalyst in said single enclosed volume;first valving to admit an intake gas into said single enclosed volume;an aqueous fluid supply system; second valving connected with saidaqueous fluid supply system and operable to admit aqueous fluid fromsaid aqueous fluid supply system and a steam reforming fuel into saidsingle enclosed volume; and a controller configured to i) cause saidfirst valving to admit a charge of intake gas into said single enclosedvolume and ii) when a predetermined condition exists in said singleenclosed volume during movement of said body to reduce the volume ofsaid single enclosed volume so as to compress said intake gas to raisepressure of said intake gas from a first pressure to a second pressure,cause said second valving to admit aqueous fluid from said aqueous fluidsupply system and an amount of said steam reforming fuel into saidsingle enclosed volume so that said aqueous fluid and steam reformingfuel absorb heat generated by said compression of said intake gas andsaid catalyst promotes a steam reformation process by which hydrogen isseparated from said steam reforming fuel or said aqueous fluid, whereinsaid combustion of said fuel and hydrogen causes movement of said bodyto increase the volume of said single enclosed volume and said movementof said body provides an energy output of said combustion chamber. 19.An internal combustion engine as claimed in claim 18, further comprisinga first reservoir to contain said steam reforming fuel and wherein saidsecond valving is connected with said first reservoir to admit saidsteam reforming fuel into said single enclosed volume.
 20. An internalcombustion engine as claimed in claim 19, wherein said first reservoir,first valving and aqueous fluid supply system are configured so thatsaid steam reforming fuel and said aqueous fluid are admitted to saidsingle enclosed volume as a mixture.
 21. An internal combustion engineas claimed in claim 19, further comprising a second reservoir to containa combustible fuel that is different to said steam reforming fuel andwherein said second valving is connected with said second reservoir andsaid controller is configured to cause said second valving to admit saidcombustible fuel into said single enclosed volume when the pressure insaid single enclosed volume is at least said second pressure to becombusted with said hydrogen.
 22. An internal combustion engine asclaimed in claim 18, wherein said steam reforming fuel is a combustiblefuel and said controller is configured to cause said second valving toadmit a second amount of said steam reforming fuel into said singleenclosed volume when the pressure in said single enclosed volume is atleast said second pressure to be com busted with said hydrogen.
 23. Aninternal combustion engine as claimed in claim 18, wherein said secondvalving comprises a first valve to admit at least one of said aqueousfluid and steam reforming fuel into said single enclosed volume and asecond valve to admit said combustible fuel into said single enclosedvolume.
 24. An internal combustion engine as claimed in claim 18,further comprising a sensor to provide signals indicative of thetemperature in said single enclosed volume and wherein said controlleris configured to control the admission of said aqueous fluid or steamreforming fuel and aqueous fluid into the single enclosed volume so asto maintain a substantially constant temperature in said single enclosedvolume.
 25. An internal combustion engine as claimed in claim 24,wherein said sensor is an optical temperature sensor.
 26. An internalcombustion chamber as claimed in claim 18, further comprising an exhaustsystem to receive exhaust gases from said combustion chamber andcooperable with said aqueous fluid supply system to extract heat fromexhaust gases flowing in said exhaust system to heat said aqueous fluidin said aqueous fluid supply system.
 27. An internal combustion engineas claimed in claim 18, wherein said aqueous fluid supply and secondvalving are configured so that said aqueous fluid is admitted to saidsingle enclosed volume as a water mist, vapour or combination of watermist and vapour.
 28. An internal combustion engine as claimed in claim18, wherein said catalyst is provided on at least one of: i) said secondvalving; ii) a combustion initiator that is operable to initiatecombustion in said combustion chamber; and iii) a wall of saidcombustion chamber.
 29. An internal combustion engine as claimed inclaim 18, wherein said body comprises: i) a reciprocating piston, or ii)a rotary member.
 30. An internal combustion engine comprising: a housingand a piston movable relative to said housing to define a combustionchamber that has a volume that is variable by movement of said pistonrelative to said housing between a top dead center position and a bottomdead center position; a catalyst provided on said piston; first valvingto admit an intake gas into said combustion chamber; an aqueous fluidsupply system; second valving connected with said aqueous fluid supplysystem and operable to admit aqueous fluid from said aqueous fluidsupply system and a steam reforming fuel into said combustion chamber;and a controller configured to i) cause said first valving to admit acharge of intake gas into said combustion chamber and ii) when apredetermined condition exists in said combustion chamber duringmovement of said piston towards said top dead center position to reducethe volume of said combustion chamber so as to compress said intake gasto raise pressure of said intake gas from a first pressure to a secondpressure cause said second valving to admit aqueous fluid from saidaqueous fluid supply system and an amount of said steam reforming fuelinto said chamber so that said aqueous fluid and steam reforming fuelabsorb heat generated by said compression of said intake gas and saidcatalyst promotes a steam reformation process by which hydrogen isseparated from said steam reforming fuel or said aqueous fluid, whereinsaid combustion of said fuel and hydrogen causes movement of said pistontowards said bottom dead center to increase the volume of saidcombustion chamber and said movement of said piston provides an energyoutput of said combustion chamber, and wherein when said second valvingis caused to admit said aqueous fluid and steam reforming fuel into saidcombustion chamber, said volume is partially defined by a wall of saidhousing that is sealingly engaged by said piston.
 31. An internalcombustion engine as claimed in claim 30, further comprising a sensor toprovide signals indicative of the temperature in said combustion chamberand wherein said controller is configured to control the admission ofsaid aqueous fluid or steam reforming fuel and aqueous fluid into thecombustion chamber so as to maintain a substantially constanttemperature in said combustion chamber.